In chemical processing which relies on fluid handling in general, and particularly when the fluids to be handled are hazardous and reactive materials, improved system leak reliability and careful integration of the fluid handling devices and network architecture into the general process system is of paramount importance. In addition, it is important that all of the component devices used in the fluid handling be well integrated into the overall fluid flow network architecture to ensure system leak reliability, provide size reduction, and enable flexible control. In applications such as semiconductor processing, for example, the fluid component devices must also exhibit particular capabilities which ensure cleanliness of the fluid delivery process, so that the solid state devices being fabricated will not be contaminated, affecting performance and reliability.
One of the most widely used fluid component devices, which has been a source of particulate contamination in the past, is the on/off valve. The fluid on/off valve must exhibit several particular capabilities. First, it must allow and prevent fluid flow, including virtually absolute shutoff to as little as about 1×10−9 cc/sec. of helium at a pressure differential of one atmosphere, as well as virtually zero outleakage (also 1×10−9 cc/sec. helium at a pressure differential of one atmosphere). Helium is typically used for leak testing because of its small atomic size, diffusivity and high mobility. This is indicative of the ability to prevent exposure of the environment of often extremely toxic and corrosive process fluids. The fluid on/off valve must also maintain the required high purity of the fluids, contributing no appreciable amount of particulates, which are typically generated by wearing parts within the wetted portion of the valve. The fluid on/off valve must possess good resistance to the corrosive properties of the fluids. Due to the toxicity of a number of the fluids transported, very high system leak reliability and long service life (avoidance of the need to shut down and change out parts) are of great importance. Also of importance are a compact design, and a reasonable cost.
During work on the present conserved space integrated fluid delivery system, an on/off valve was designed which provides many of the advantages discussed above. In addition to the description of the integrated fluid delivery system, that on/off valve is described in detail herein.
The present invention takes the concepts regarding an integrated fluid flow system to a new level of integration which permits not only improved functionality, but also considerable cost savings in fabrication. As a result of the reduced fabrication cost, and a properly balanced level of modularity, it is possible to reduce maintenance costs for the fluid flow system by replacing integrated modules rather than shutting the system down for long maintenance and repair operations with respect to individual component devices (which are part of the integrated module in present designs).
The importance of very high system leak reliability and long service life (avoidance of the need to shut down and change out parts) in the semiconductor industry is illustrated by the factors which must be considered with respect to the design of an on/off valve. For example, in a fluid flow valve, each of the fluid-wetted parts must be fabricated from a highly corrosion-resistant material. In the general chemical processing industry, process control valves frequently employ corrosion-resistant plastic or elastomeric valve seats. Metal valve seats provide advantages in terms of minimizing valve seat maintenance and maintaining fluid cleanliness; however, metal valve seats require high seating forces, compared to polymeric seats, in order to reliably provide a tight shut-off. As a result, all valves with metal valve seats are typically larger in size and cost significantly more than valves with polymeric seats. Additional advantages of all-metal valves include their ability to be heated to high temperatures and their superior moisture dry-down characteristics.
One example of an advantageous valve having metal-to-metal seating for controlling the flow of a gas employs a flexible metal diaphragm mounted in the valve so the diaphragm can be moved into and out of sealing contact with the metal seat to close and open a gas passage, respectively. The valve seat has a rounded metal sealing projection with a relatively small cross-sectional radius around the seating section extending about the gas flow passage. The flexible metal diaphragm is moved into and out of sealing contact with the metal sealing projection of the seat by an actuator which employs a metal backing member which forcefully contacts the diaphragm during narrowing or closing of the gas flow passage. For additional information about this all-metal valve, one skilled in the art should refer to U.S. Pat. No. 5,755,428, of Louis Ollivier, issued May 26, 1988.
As described above, the potential problems of process fluid outleakage and/or process fluid attack on valve mechanicals may be addressed using a diaphragm valve having metal wetted parts (among other closing techniques). However, in previous designs, when the valve seat is metal, a particularly high seating force is required, compared with polymeric valve seats. Typically, when a plastic seat is used for a high cycle application, plastic deformation of the seat leads to lower valve reliability. The valve is typically operated in a normally-closed position, to provide a “fail safe” condition in the event of a loss of motive power (electric or pneumatic) to the actuator. When the actuator design incorporates a spring (or springs) capable of applying the large force required for a metal valve seat, the spring is typically large, on the order of 3 cm to 10 cm tall, and the valve itself is expensive, often costing around 5-6 times the price of a comparable capacity plastic-seated valve. It would be highly desirable to have a corrosion-resistant on/off valve, where all of the fluid-wetted parts are metal; where the valve is compact in design, and well integrated into its end use application.
With respect to an integrated network architecture of fluid flow devices and channels with an integrated control system, there is a constant need for a higher degree of integration, simplification and ease of operation. In addition to performance and handling advantages, the integrated fluid flow system must be cost competitive. This means that fabrication methods for the various fluid handling devices, interconnecting network architecture and integrated control system need to be easily scalable in tooling for mass production, variable production demand and cost-effective NRE (Non-recurring Engineering) charges. The present invention provides substantial advantages in all of these areas.